Micro-tube/multi-port counter flow radiator design for electronic cooling applications

ABSTRACT

A counter flow radiator includes multiple layered cooling cores configured in series along a first direction that is the same as the direction of airflow used to cool fluid flowing through the counter flow radiator. Heated fluid inputs the counter flow radiator at a first end and flows through each cooling core in a serpentine-like path to the second end of the counter flow radiator, effectively progressing in a direction opposite that of the airflow.

RELATED APPLICATIONS

This Patent Application claims priority under 35 U.S.C. 119 (e) of the co-pending U.S. Provisional Patent Application Ser. No. 60/927,424, filed May 2, 2007, and entitled “MICRO-TUBE/MULTI-PORT COUNTER FLOW RADIATOR DESIGN FOR ELECTRONIC COOLING APPLICATIONS”. The Provisional Patent Application Ser. No. 60/927,424, filed May 2, 2007, and entitled “MICRO-TUBE/MULTI-PORT COUNTER FLOW RADIATOR DESIGN FOR ELECTRONIC COOLING APPLICATIONS” is also hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to an apparatus for cooling a heat producing device in general, and specifically, to a fluid-air heat exchanger used in fluid cooling applications.

BACKGROUND OF THE INVENTION

Cooling of high performance integrated circuits with high heat dissipation is presenting significant challenge in the electronics cooling arena. Conventional cooling with heat pipes and fan mounted heat sinks are not adequate for cooling chips with ever increasing wattage requirements.

A particular problem with cooling integrated circuits within electronic devices is that more numerous and powerful integrated circuits are configured within the same size or smaller chassis. As more powerful integrated circuits are developed, each with an increasing density of heat generating transistors, the heat generated by each individual integrated circuit continues to increase. Further, more and more integrated circuits, such as graphics processing units, microprocessors, and multiple-chip sets, are being added to electronic devices, such as electronics servers and personal computers. Still further, the more powerful and more plentiful integrated circuits are being added to the same, or smaller size chassis, thereby increasing the per unit heat generated for these devices. In such configurations, conventional chassis' provide limited dimensions within which to provide an adequate cooling solution. Conventionally, the integrated circuits are cooled using a heat sink and a large fan that blows air over the heat sink, or simply by blowing air directly over the circuit boards containing the integrated circuits. However, considering the limited free space within the device chassis, the amount of air available for cooling the integrated circuits and the space available for conventional cooling equipment, such as heat sinks and fans, is limited.

Closed loop liquid cooling presents alternative methodologies for conventional cooling solutions. Closed loop liquid cooling solutions more efficiently reject heat to the ambient than air cooling solutions. A closed loop cooling system includes a cold plate to receive heat from a heat source, a radiator with fan cooling for heat rejection, and a pump to drive liquid through the closed loop. The design of each component is often complex and requires detailed analysis and optimization for specific applications.

FIG. 1 illustrates a first conventional radiator 2 configured with one-direction fluid flow. The radiator 2 is configured with a fluid input header 10, a fluid output header 12, a set of parallel fluid channels 14 through which heated fluid flows, and a set of cooling fins 16 thermally coupled to the set of fluid channels 14. Heated fluid enters the fluid input header 10 and flows into the fluid channels 14. The fluid channels 14 and the cooling fins 16 are made of a thermally conductive material to enhance heat transfer from the fluid flowing through the fluid channels 14 to the cooling fins 16. The cooling fins 16 are exposed to airflow for cooling. The airflow is provided in a direction that is perpendicular to a fluid flow direction of the fluid flowing through the fluid channels 14. In this configuration, each of the fluid channels 14 is exposed to the same temperature airflow. As the fluid temperature in each of the fluid channels 14 is the same, and the air temperature intersecting each of the fluid channels 14 is the same, the temperature difference between the fluid temperature and the air temperature is the same for each fluid channel 14. Cooled fluid flows from the fluid channels 14 to the fluid output header 12 and exits the radiator 2.

FIG. 2 illustrates a second conventional radiator 4 configured with two-direction fluid flow. The radiator 4 is configured with a first fluid header 20, a second fluid header 22, a first set of parallel fluid channels 24, a second set of parallel fluid channels 25, and a set of cooling fins 26 thermally coupled to the first set of fluid channels 24 and the second set of fluid channels 25. The first set of fluid channels 24 are parallel to the second set of fluid channels 25. Heated fluid enters the first fluid header 20 and flows into the first set of fluid channels 24. The first fluid header 20 includes a fluid divider 28 configured to prevent fluid input to the first fluid header 20 from entering the second set of fluid channels 25 via the first fluid header 20. The fluid channels 24 and the cooling fins 26 are made of a thermally conductive material to enhance heat transfer from the fluid flowing through the fluid channels 24 to the cooling fins 26. The cooling fins 26 are exposed to airflow for cooling. Cooled fluid flows from the fluid channels 24 to the second fluid header 22 and is directed into the fluid channels 25. The fluid channels 25 are made of a thermally conductive material to enhance heat transfer from the fluid flowing through the fluid channels 25 to the cooling fins 26. Further cooled fluid flows from the fluid channels 25 to the first fluid header 20 and exits the radiator 4. The fluid divider 28 prevents fluid exiting the fluid channels 25 from recirculating into the fluid channels 24.

As in the first conventional radiator 2, the airflow is provided to the second conventional radiator 4 in a direction that is perpendicular to a fluid flow direction of the fluid flowing through the fluid channels 24, 25. In this configuration, each of the fluid channels 24, 25 is exposed to the same temperature airflow. However, the fluid flowing through the second set of fluid channels 25 is cooler relative to the fluid flowing through the first set of fluid channels 24. Since the air temperature of the airflow intersecting each of the fluid channels 24, 25 is the same, there is a greater temperature difference between the airflow and the fluid flowing through the first set of channels 24 then the temperature difference between the airflow and the fluid flowing through the second set of fluid channels 25. Therefore, the cooling efficiency of the radiator 4 is non-uniform.

The performance of the radiator depends on an air flow rate over the cooling fins, a fluid flow rate through the fluid channels, a surface area of the cooling fins, and the difference in temperature between the air and the fluid.

What is needed is a more efficient cooling methodology for cooling integrated circuits within electronic devices. What is also needed is a cooling methodology that increases cooling performance within a given space constraint.

SUMMARY OF THE INVENTION

A counter flow radiator is air cooled and is applicable for fluid cooling in electronic systems. Heated fluid, such as heated liquid or two-phase fluid, enters the counter flow radiator and travels through a fluid path including multiple micro-conduits, such as micro-tubes, micro-channels, or micro-ports, while rejecting the heat from the fluid into fin assemblies coupled to the micro-conduits. Airflow is directed over the surface of the fin assemblies to remove heat from the fin assemblies to the air. The counter flow radiator is configured with multiple cooling cores. Each cooling core includes at least one layer of micro-conduits and at least one layer of cooling fin assemblies alternatively stacked on top of each other. The cooling cores are coupled together in series along a first direction. The airflow is also directed along the first direction. The fins are aligned in the direction of air flow. The heated fluid enters the counter flow radiator through one or more inlet points in a first header. The one or more inlet points are positioned on an air exhaust side of the counter flow radiator. The heated fluid follows a serpentine-like path that passes though the multiple cooling cores, crossing the air flow path multiple times, and leaves the counter flow radiator through one or more outlet points in a second header. The one or more outlet points are positioned on an air intake side of the counter flow radiator. One or both of the headers, depending on the number of cooling cores, include a divider or dividers that selectively separates the multiple cooling cores and facilitate the serpentine-like fluid path. The counter flow radiator configuration improves the thermal efficiency of the radiator by flowing fluid in an opposite direction of airflow, thereby exposing the hottest temperature fluid to the hottest temperature air and the coldest temperature fluid to the coldest temperature air. In some embodiments of the counter flow radiator, a constant temperature differential exists in the direction of air flow, across the width of the heat sink

In one aspect, a fluid-air heat exchanger includes a plurality of fluid-air cooling cores, a first fluid header, and a second fluid header. Each cooling core includes at least one layer of one or more thermally conductive fluid conduits and at least one layer of thermally conductive cooling fins coupled to at least one fluid conduit layer, wherein each fluid conduit is configured along a first direction from a first end of the cooling core to a second end of the cooling core, further wherein the plurality of cooling cores are stacked side by side along a second direction perpendicular to the first direction such that the fluid conduits of the plurality of cooling cores are configured in parallel. The first fluid header is coupled to the first end of each cooling core, wherein the first header includes an inlet port configured to receive an input fluid. The second header is coupled to the second end of each cooling core, wherein the first header and the second header are configured to direct fluid flow in series from a first cooling core closest to the inlet port of the first header to each successively stacked cooling core along the second direction.

A second cooling core is positioned furthest from the first cooling core within the plurality of stacked cooling cores. In some embodiments, the second cooling core is configured to receive an intake airflow into the fluid-air heat exchanger along the second direction and the first cooling core is configured to exhaust the airflow from the fluid-air heat exchanger. If a number of cooling cores is even, then the first fluid header includes an outlet port configured to output fluid received from the second cooling core. In this configuration, the first header includes at least one divider to separate the inlet port from the outlet port. If a number of cooling cores is odd, then the second fluid header includes an outlet port configured to output fluid received from the second cooling core. In this configuration, the first header and the second header cumulatively include at least one fluid divider configured to direct fluid flow from the inlet port to the outlet port via the plurality of cooling cores. The fluid flows between the first header, the second header, and from cooling core to cooling core in a serpentine-like manner. In some embodiments, a temperature of the input fluid is greater than a temperature of the fluid output from the outlet port. In this case, a hot-to-cold fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core. In some embodiments, a temperature of the intake airflow is colder than a temperature of the exhaust airflow. In this case, a hot-to-cold air temperature gradient is formed along the second direction from the first cooling core to the second cooling core.

In some embodiments, a temperature of the input fluid is less than a temperature of the fluid output from the outlet port, and a temperature of the intake airflow is greater than a temperature of the exhaust airflow. In this case, a cold-to-hot fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core, and a cold-to-hot air temperature gradient is formed along the second direction from the first cooling core to the second cooling core. Each cooling core is exposed to a different temperature airflow.

In some embodiments, the inlet port is positioned proximate a first end of the first fluid header, and the first cooling core is positioned proximate the first end of the first fluid header and a first end of the second fluid header. The second cooling core is positioned proximate a second end of the first fluid header and a second end of the second fluid header. Each layer of fluid conduits can include a plurality of individual thermally conductive micro-tubes, wherein each micro-tube is configured such that fluid flow therethrough is isolated from each other micro-tube. Alternatively, each layer of fluid conduits can include a plurality of individual thermally conductive micro-tubes, wherein each micro-tube includes one or more common openings with an adjacent micro-tube such that fluid flow therethrough is intermixed between adjacent micro-tubes. Each cooling fin is configured along the second direction. In some embodiments, each cooling core includes a plurality of core layers, each layer including at least one layer of cooling fins and a layer of at least one fluid conduit, further wherein each core layer within a given cooling core is stacked along a third direction that is perpendicular to the first direction and perpendicular to the second direction.

In another aspect, the fluid-air heat exchanger is included within a fluid-based cooling system. The fluid based cooling system includes the fluid-air heat exchanger, one or more air movers configured to provide the intake airflow to the fluid-air heat exchanger, and a fluid-based cooling loop coupled to the fluid-air heat exchanger, wherein the cooling loop is configured to provide heated fluid to inlet port of the first fluid header.

In yet another aspect, the fluid-air heat exchanger has a concurrent flow configuration in which the fluid inlet is on the same side of the heat exchanger as the air flow intake side.

Other features and advantages of the present invention will become apparent after reviewing the detailed description of the embodiments set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first conventional radiator configured with one-direction fluid flow.

FIG. 2 illustrates a second conventional radiator configured with two-direction fluid flow.

FIG. 3 illustrates an exemplary block diagram of a cooling system including a counter flow radiator coupled to a fluid-based cooling loop.

FIG. 4 illustrates a cut-out perspective view of an exemplary configuration of the counter flow radiator.

FIG. 5 illustrates a cut-out, top down view of the counter flow radiator including the air and fluid flow directions.

FIG. 6 illustrates a cut-out side view of the first fluid header including a flow divider.

FIG. 7 illustrates a cut-out side view of the second fluid header.

FIG. 8 illustrates a cut-out, top-down view of a first exemplary fluid conduit configured such that each micro-conduit is isolated from each other.

FIG. 9 illustrates a cut-out, top-down view of a second exemplary fluid conduit configured where each micro-conduit is configured to enable fluid intermixing.

FIG. 10 illustrates the counter flow radiator of FIG. 5 reconfigured to cool an input air flow.

FIG. 11 illustrates the radiator of FIG. 5 reconfigured for concurrent flow.

The present invention is described relative to the several views of the drawings. Where appropriate and only where identical elements are disclosed and shown in more than one drawing, the same reference numeral will be used to represent such identical elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Embodiments of the present invention are directed to a counter flow fluid-air heat exchanger included within a fluid-based cooling system, where the cooling system removes heat generated by one or more heat generating devices within an electronics device or system. The heat generating devices include, but are not limited to, one or more central processing units (CPU), a chipset used to manage the input/output of one or more CPUs, one or more graphics processing units (GPUs), and/or one or more physics processing units (PPUs), mounted on a motherboard, a daughter card, and/or a PC expansion card. The cooling system can also be used to cool power electronics, such as mosfets, switches, and other high-power electronics requiring cooling. In general, the cooling system described herein can be applied to any electronics sub-system that includes a heat generating device to be cooled.

In some embodiments, the counter flow fluid-air heat exchanger is a radiator. As described herein, reference to a radiator is used. It is understood that reference to a radiator is representative of any type of fluid-air heat exchanging system unless specific characteristics of the radiator are explicitly referenced.

Heat generated from a heat generating device is received by a heat exchanger. In some embodiments, the heat exchanger is configured with fluid channels through which fluid in the cooling loop passes. As the fluid passes through the heat exchanger, heat is passed to the fluid, and heated fluid is output from the heat exchanger and directed to the counter flow radiator. One or more air movers, such as fans, are coupled to the counter flow radiator. The heated fluid is input to the counter flow radiator. Airflow provided by the air mover is directed over and through the counter flow radiator, thereby cooling the fluid passing therethrough. Cooled fluid is output from the counter flow radiator.

FIG. 3 illustrates an exemplary block diagram of a cooling system 100 including a counter flow radiator coupled to a fluid-based cooling loop. The cooling loop includes the counter flow radiator 30, a pump 90, and a heat exchanger 92, each coupled via fluid lines 94, 96, 98. In this configuration, the cooling loop is coupled to a radiator inlet via fluid line 94 and to a radiator outlet via fluid line 96. It is understood that the relative position of each component in the cooling loop is for exemplary purposes only. For example, the pump 90 can be positioned on the inlet side of the counter flow radiator 30, instead of the outlet side as shown in FIG. 3. One or more air movers (not shown), such as fans, are coupled to the counter flow radiator 30 so as to provide airflow to an intake side of the counter flow radiator 30.

The heat exchanger 92 is coupled to a heat generating device 102. Any conventional coupling means can be used to couple the heat exchanger 92 to the heat generating device 102. A removable coupling means is used to enable the heat exchanger to be removed and reused. Alternatively, a non-removable coupling means is used. Heat generated by the heat generating device 102 is transferred to fluid flowing through the heat exchanger 92. The heated fluid is output from the heat exchanger 92 and input to the counter flow radiator 30. Although the cooling loop includes a single heat exchanger 92, the cooling loop can include more than one heat exchanger coupled in series or parallel to the heat exchanger 92. In this manner, the cooling loop can be used to cool multiple heat generating devices, where the multiple heat generating devices are all coupled to a single circuit board or are distributed on multiple circuit boards.

The counter flow radiator includes multiple layered cooling cores configured in series along a first direction that is opposite the direction of airflow used to cool fluid flowing through the counter flow radiator. Heated fluid inputs the counter flow radiator at a first end and flows through each cooling core in a serpentine-like path to a second end of the counter flow radiator, effectively progressing in a direction opposite that of the airflow. As described herein, reference is made to a counter flow radiator that includes two layered cooling cores, although the counter flow radiator can include more than two layered cooling cores.

FIG. 4 illustrates a cut-out perspective view of an exemplary configuration of the counter flow radiator 30. The counter flow radiator 30 includes two layered cooling cores 50, 52 coupled width-wise in series, a first fluid header 32, and a second fluid header 34 (FIG. 5). As shown in FIG. 4, the second fluid header 34 is removed to show a cut out side view of the cooling cores 50, 52. Each cooling core 50, 52 includes at least one fluid conduit 38 and at least one layer of cooling fin assemblies 36 thermally coupled to the fluid conduit 38. As shown in FIG. 4, each cooling core 50, 52 includes three layers of fluid conduits 38 and four layers of cooling fin assemblies 36. It is understood that each cooling core can include more or less than the number of fluid conduit layers and cooling fin assembly layers than those shown in FIG. 4. The fluid conduits 38 and the cooling fin assemblies 36 are each made of thermally conductive material such that heat is transferred from the fluid flowing through the fluid conduits 38 to the material of the fluid conduits 38, and the heat is further transferred from the material of the fluid conduits 38 to the cooling fin assemblies 36. The fluid conduits 38 can be made of the same or different thermally conductive material(s) as the cooling fin assemblies 36.

Each cooling core is aligned in series along a first direction, indicated as the x-axis in FIG. 4. Each fin in the fin assembly 36 is also aligned in the first direction. Each fin is continuous across all of the cooling cores 50, 52. Alternatively, each fin includes multiple segments aligned along the first direction. Each fluid conduit 38 extends lengthwise through the cooling core, referred to as a second direction that is indicated as the y-axis in FIG. 4. Each fluid conduit 38 includes multiple micro-conduits 46. Each micro-conduit 46 is made of a thermally conductive material. A first end of each micro-conduit 46 within the fluid conduit 38 is coupled to the first fluid header 32, and a second end of each micro-conduit 46 is coupled to the second fluid header 34 (FIG. 5).

The aligned cooling cores 50, 52 form an intake side 31 and an exhaust side 33. One or more fluid inlets 40 are positioned proximate the exhaust side 33 of the first fluid header 32. If the counter flow radiator includes an even number of cooling cores, as is the case of the counter flow radiator 30 in FIG. 4, then one or more fluid outlets 42 (FIG. 5) are positioned proximate the intake side 31 of the first fluid header 32. If the counter flow radiator includes an odd number of cooling cores, then one or more fluid outlets are positioned proximate the intake side 31 of the second fluid header.

The first fluid header 32 is configured to direct fluid entering from the fluid inlet 40 into the first end of the micro-conduits 46 of the cooling core 50, and to direct fluid exiting from the first end of the micro-conduits 46 of the cooling core 52 into the fluid outlet 42 (FIG. 5). The first fluid header 32 is also configured to prevent fluid entering from the fluid inlet 40 from bypassing the cooling core 50 and flowing directly to the fluid outlet 42 (FIG. 5). FIG. 6 illustrates a cut-out side view of the first fluid header 32 including a flow divider 44. The flow divider 44 prevents fluid entering from the fluid inlet 40 from bypassing the micro-conduits 46 of the cooling core 50 and flowing directly to the fluid outlet 42 (FIG. 5).

The second fluid header 34 (FIG. 5) is configured to direct fluid exiting from the second ends of the micro-conduits 46 of the cooling core 50 into the second ends of the micro-conduits 46 of the cooling core 52, thereby forming a fluid path from the cooling core 50 to the cooling core 52. As such, the second fluid header 34 does not include a flow divider. FIG. 7 illustrates a cut-out side view of the second fluid header 34. As compared to the first fluid header 32 in FIG. 6, the second fluid header 34 in FIG. 7 does not include a flow divider, thereby providing fluidic access between the second ends of the micro-conduits 46 in cooling core 50 and the second ends of the micro-conduits 46 in the cooling core 52.

If additional cooling cores are added to the counter flow radiator, a corresponding number of flow dividers are also added. For example, if a third cooling core is coupled in series to the cooling core 52, then a flow divider is added to the second fluid header between the second cooling core 52 and the third cooling core so as to prevent fluid exiting the second end of the micro-conduits 46 in the cooling core 50 from bypassing the second ends of the micro-conduits 46 in the cooling core 52. In this example, another flow divider is not added to the first fluid header. Instead, the portion of the first fluid header that receives fluid exiting from the micro-conduits 46 in the second cooling core 52 is extended to couple with the first ends of the micro-conduits 46 in the third cooling core, thereby enabling fluid to flow from the first ends of the micro-conduits 46 in the second cooling core 52 into the first ends of the micro-conduits 46 in the third cooling core. In this exemplary case, the first fluid header is not configured with the fluid outlet 42. Instead, the fluid outlet is configured on the second fluid header. Each of the fluid headers is adapted in a similar manner for each additional cooling core added to the counter flow radiator. In general, a flow divider provides a means for preventing fluid flow. As such, the flow divider can be implemented as a wall within the header, or the header itself can be comprised of multiple separate header components coupled together, where an interface between two adjoining header components forms a flow divider.

FIG. 5 illustrates a cut-out, top down view of the counter flow radiator 30 including the air and fluid flow directions. Heated fluid is input to the counter flow radiator 30 at the fluid inlet 40. The fluid inlet 40 is positioned proximate to the exhaust side 33. The heated fluid flows first into the cooling core that forms the exhaust side 33, which in this case is the cooling core 50. The fluid flows through the fluid conduits 38 in the cooling core 50 along the second direction, which in this case is the negative y-direction. As fluid exits the fluid conduits 38 in the cooling core 50, the fluid is directed along the first direction, which in this case is the positive x-direction, to the fluid conduits 38 in the cooling core 52 via the second fluid header 34. The fluid flows through the fluid conduits 38 in the cooling core 52 opposite the second direction, which in this case is the positive y-direction. As fluid exits the fluid conduits 38 in the cooling core 52, the fluid is directed out of the fluid outlet 42 via the first fluid header 32. In this manner, the fluid flows in a serpentine-like direction, back and forth along the second direction while progressing along the first direction. As the heated fluid flows through the fluid conduits, heat is transferred from the fluid to the cooling fin assemblies 36. The fluid begins to cool as it flows through the cooling core 50, and the fluid continues to cool as it passes through the cooling core 52 so that the fluid flowing through the cooling core 50 is hotter than the fluid flowing through the cooling core 52. The coldest fluid is the fluid output from the counter flow radiator 30, and the hottest fluid is the fluid input to the counter flow radiator.

Airflow directed at the counter flow radiator 30 is input at the intake side 31 and output at the exhaust side 33. In this manner, airflow is directed through the cooling cores 50, 52 opposite the first direction, that is the negative x-direction. As the air passes over the cooling fin assemblies 36, heat is transferred from the cooling fin assembles 36 to the air. Therefore, the further the air passes through the counter flow radiator 30, the hotter the air becomes. The coldest air is the air at the intake side 31 of the counter flow radiator 30, and the hottest air is the air output at the exhaust side 33 of the counter flow radiator. The fluid at the intake side is exposed to cooler air than the fluid at the exhaust side because the air at the exhaust side has been heated from fluid it has passed while passing from the intake side to the exhaust side.

Each fluid conduit 38 includes a plurality of micro-conduits 46. In some embodiments, each of the micro-conduits 46 are isolated from each other and fluid flowing through each micro-conduit 46 does not intermix with fluid flowing within each of the other micro-conduits 46.

FIG. 8 illustrates a cut-out, top-down view of a first exemplary fluid conduit configured such that each micro-conduit 46 is isolated from each other. In this case, the fluid intermixes at each fluid header as the fluid exits the micro-conduits 46, for example at the fluid header 34. The micro-conduits 46 are made of thermally conductive material that enables heat transfer with the fluid flowing through the micro-conduits 46.

As there are fluid and air temperature gradients from the intake side of the counter flow radiator to the exhaust side, there are also fluid and air temperature gradients within the fluid conduit 38 of each cooling core. Fluid flowing in the micro-conduits located closer to the exhaust side of the counter flow radiator interact act with hotter air than fluid flowing in the micro-conduits closer to the intake side of the counter flow radiator. If the fluid conduit 38 is configured with isolated micro-conduits 46, as in the configuration shown in FIG. 8, then a fluid temperature gradient exists between the intake side and the exhaust side within a given fluid conduit. In some embodiments, the fluid conduit 38 is configured as a single channel, without micro-conduits. In this configuration, fluid is not isolated to one position relative to the intake side and the exhaust side, and intermixing of the fluid from the intake side to the exhaust side occurs as the fluid flows through the fluid conduit 38. Although sufficient intermixing may or may not occur to completely eliminate the fluid temperature gradient between the intake side and the exhaust side, the fluid temperature gradient in the single channel configuration is less than the fluid temperature gradient in the isolated micro-conduit configuration.

A disadvantage of the single channel configuration is a reduction in the thermal transfer rate between the fluid and the fluid conduit relative to the micro-conduit configuration. The surface area of the micro-conduits 46 enhance the heat transfer rate, as compared to the single channel configuration, because of the larger heat transfer surface area of all the micro-conduits 46.

In an alternative configuration, each micro-conduit is configured with side openings that match side openings of adjacent micro-conduits, thereby enabling intermixing of fluid between micro-conduits as the fluid flows through the fluid conduit. FIG. 9 illustrates a cut-out, top-down view of a second exemplary fluid conduit configured such that each micro-conduit 46′ is configured to enable fluid intermixing. Each of the micro-conduits 46′ is configured with micro-conduit openings 48. Adjacent micro-conduits 46′ are configured with matching micro-conduit openings 48 such that fluid flowing through adjacent micro-conduits 46′ intermixes via the micro-conduit openings 48. It is understood that the positions of the micro-conduit openings 48 shown in FIG. 9 are for exemplary purposes only. The number and position of micro-conduit openings can be configured into any pattern, random or non-random, so as to achieve desired fluid intermixing effects.

The micro-conduits with openings configuration reduces the fluid temperature gradient within the fluid conduit relative to the isolated micro-conduit configuration. However, if the number of micro-conduits is the same in both the isolated micro-conduit configuration and the micro-conduits with openings configuration, then there is a reduction in micro-conduit surface area in the micro-conduits with openings configuration relative to the isolated micro-conduit configuration. A reduction in surface area reduces the thermal transfer rate between the fluid and the micro-conduits. To increase the surface area, the fluid conduit can be configured with a greater number of micro-conduits. A fluid conduit including micro-conduits with openings can be configured with the same surface area as a corresponding fluid conduit with isolated micro-conduits be increasing the number of micro-conduits with openings. In general, the surface area used to perform thermal transfer can be adjusted in this manner, whether the micro-conduits are configured as isolated micro-conduits or micro-conduits with openings.

In general, the thermal efficiency of the counter flow radiator is constrained by the system temperature difference between the input fluid temperature at the exhaust side and the input air temperature at the intake side. There are diminishing returns for each added cooling core. As more cooling cores are added, the cooling core temperature difference (the difference between the fluid temperature and the air temperature input to the cooling core) is diminished for each cooling core in the system. So even though the overall total efficiency of the counter flow radiator is increased (to a maximum value limited by the system temperature difference), the efficiency of each cooling core is diminished with each added cooling core.

The thermal efficiency of the counter flow radiator can be adjusted by adjusting the fluid flow rate through counter flow radiator. The slower the flow rate provides a greater fluid temperature difference between the input fluid temperature and the output fluid temperature because there is a longer time period for the fluid to be exposed to the thermal transfer occurring within the counter flow radiator. However, the fluid flow rate must also be determined and balanced against the flow rate conditions necessary to optimize the heat transfer occurring within the heat exchanger, where heat is transferred to the fluid from the heat generating device. In general, the fluid flow rate can be optimized to achieve the desired system thermal performance and/or desired cooling core temperature difference for each cooling core.

The counter flow radiator is described above in terms of cooling a heated fluid. Specifically, the counter flow radiator receives a heated fluid as input, cools the heated fluid within the radiator, and outputs a cooled fluid. The heated fluid is cooled using a fluid-to air cooling method in which an input air flow passes through the radiator, and heat from the fluid flowing within the radiator passes from the fluid, to the radiator material, and to the air passing over the radiator material. As such, air flow out of the radiator is hotter than the air flow input to the radiator. In an alternative embodiment, the counter flow radiator is configured to cool heated air. In this alternative embodiment, a cold fluid, such as a refrigerant, is input into the counter flow radiator and input air passes through the radiator. Heat is transferred from the input air to the cold fluid flowing through the radiator. As such, air flow out of the radiator is cooler than the air flow input to the radiator. Fluid output from the radiator is hotter than the fluid input into the radiator.

FIG. 10 illustrates the counter flow radiator of FIG. 5 reconfigured to cool an input air flow. Cold fluid is input to the counter flow radiator at the fluid inlet 40. The cold fluid flows through the cooling cores 50 and 52, and is output via the fluid outlet 42 in a similar manner as that described in relation to FIG. 5. Heated air flow is directed into the counter flow radiator at the intake side 31. As the air flow passes through the cooling cores 52 and 50, heat is transferred from the air flow to the cold fluid flowing through the cooling cores 52 and 50. Cooled air is output from the counter flow radiator at the exhaust side 33. Heated fluid is output from the counter flow radiator at the fluid outlet 42.

The counter flow radiator is described above in terms of a “counter flow” configuration in which the air intake side of the radiator is opposite that of the fluid inlet. In an alternative embodiment, the radiator is configured as concurrent flow, or “co-flow”, in which either the fluid flow direction through the radiator is reversed or the air flow direction through the radiator is reversed in comparison to the counter flow radiator. Specifically, in this alternative embodiment, the fluid inlet and the air flow intake side are on the same side of the radiator, and the fluid outlet and the air flow exhaust side are on the same side of the radiator.

FIG. 11 illustrates the radiator of FIG. 5 reconfigured for concurrent flow. Heated fluid is input to the concurrent flow radiator at the fluid inlet 40. The heated fluid flows through the cooling cores 50 and 52, and is output via the fluid outlet 42 in a similar manner as that described in relation to FIG. 5. Air flow is directed into the radiator at the side 33. As the airflow passes through the cooling cores 50 and 52, heat is transferred from the heated fluid to the air flow passing through the cooling cores 50 and 52. Heated air is output from the radiator at the side 31. Cooled fluid is output from the radiator at the fluid outlet 42.

Similarly to the counter flow radiator of FIG. 10, the concurrent flow radiator of FIG. 11 can be configured to cool heated air. In this alternative embodiment, a cold fluid is input into the concurrent flow radiator and input heated air passes through the radiator, where the air intake side is on the same side of the radiator as the fluid inlet. Heat is transferred from the heated air to the cold fluid flowing through the radiator. As such, air flow out of the radiator is cooler than the air flow input to the radiator. Fluid output from the radiator is hotter than the fluid input into the radiator.

The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention. 

1. A fluid-air heat exchanger comprising: a. a plurality of fluid-air cooling cores, each cooling core includes at least one layer of one or more thermally conductive fluid conduits and at least one layer of thermally conductive cooling fins coupled to at least one fluid conduit layer, wherein each fluid conduit is configured along a first direction from a first end of the cooling core to a second end of the cooling core, further wherein the plurality of cooling cores are stacked side by side along a second direction perpendicular to the first direction such that the fluid conduits of the plurality of cooling cores are configured in parallel; b. a first fluid header coupled to the first end of each cooling core, wherein the first header includes an inlet port configured to receive an input fluid; and c. a second header coupled to the second end of each cooling core, wherein the first header and the second header are configured to direct fluid flow in series from a first cooling core closest to the inlet port of the first header to each successively stacked cooling core along the second direction, wherein a second cooling core positioned furthest from the first cooling core within the plurality of stacked cooling cores is configured to receive an intake airflow into the fluid-air heat exchanger along the second direction and the first cooling core is configured to exhaust the airflow from the fluid-air heat exchanger.
 2. The fluid-air heat exchanger of claim 1 wherein if a number of cooling cores is even, then the first fluid header includes an outlet port configured to output fluid received from the second cooling core.
 3. The fluid-air heat exchanger of claim 2 wherein the first header includes at least one divider to separate the inlet port from the outlet port.
 4. The fluid-air heat exchanger of claim 1 wherein if a number of cooling cores is odd, then the second fluid header includes an outlet port configured to output fluid received from the second cooling core.
 5. The fluid-air heat exchanger of claim 1 wherein the first header and the second header cumulatively include at least one fluid divider configured to direct fluid flow from the inlet port to the outlet port via the plurality of cooling cores.
 6. The fluid-air heat exchanger of claim 5 wherein the fluid flows between the first header, the second header, and from cooling core to cooling core in a serpentine-like manner.
 7. The fluid-air heat exchanger of claim 1 wherein a temperature of the input fluid is greater than a temperature of the fluid output from the outlet port.
 8. The fluid-air heat exchanger of claim 7 wherein a hot-to-cold fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 9. The fluid-air heat exchanger of claim 7 wherein a temperature of the intake airflow is colder than a temperature of the exhaust airflow.
 10. The fluid-air heat exchanger of claim 7 wherein a hot-to-cold air temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 11. The fluid-air heat exchanger of claim 1 wherein a temperature of the input fluid is less than a temperature of the fluid output from the outlet port.
 12. The fluid-air heat exchanger of claim 11 wherein a cold-to-hot fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 13. The fluid-air heat exchanger of claim 11 wherein a temperature of the intake airflow is greater than a temperature of the exhaust airflow.
 14. The fluid-air heat exchanger of claim 11 wherein a cold-to-hot air temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 15. The fluid-air heat exchanger of claim 1 wherein each cooling core is exposed to a different temperature airflow.
 16. The fluid-air heat exchanger of claim 1 wherein the inlet port is positioned proximate a first end of the first fluid header, and the first cooling core is positioned proximate the first end of the first fluid header and a first end of the second fluid header.
 17. The fluid-air heat exchanger of claim 16 wherein the second cooling core is positioned proximate a second end of the first fluid header and a second end of the second fluid header.
 18. The fluid-air heat exchanger of claim 1 wherein each layer of fluid conduits comprises a plurality of individual thermally conductive micro-tubes, wherein each micro-tube is configured such that fluid flow therethrough is isolated from each other micro-tube.
 19. The fluid-air heat exchanger of claim 1 wherein each layer of fluid conduits comprises a plurality of individual thermally conductive micro-tubes, wherein each micro-tube includes one or more common openings with an adjacent micro-tube such that fluid flow therethrough is intermixed between adjacent micro-tubes.
 20. The fluid-air heat exchanger of claim 1 wherein each cooling fin is configured along the second direction.
 21. The fluid-air heat exchanger of claim 1 wherein each cooling core includes a plurality of core layers, each layer including at least one layer of cooling fins and a layer of at least one fluid conduit, further wherein each core layer within a given cooling core is stacked along a third direction that is perpendicular to the first direction and perpendicular to the second direction.
 22. A fluid-air heat exchanger comprising: a. a plurality of fluid-air cooling cores, each cooling core includes at least one layer of one or more thermally conductive fluid conduits and at least one layer of thermally conductive cooling fins coupled to at least one fluid conduit layer, wherein each fluid conduit is configured along a first direction from a first end of the cooling core to a second end of the cooling core, further wherein the plurality of cooling cores are stacked side by side along a second direction perpendicular to the first direction such that the fluid conduits of the plurality of cooling cores are configured in parallel; b. a first fluid header coupled to the first end of each cooling core, wherein the first header includes an inlet port configured to receive an input fluid; and c. a second header coupled to the second end of each cooling core, wherein the first header and the second header are configured to direct fluid flow in series from a first cooling core closest to the inlet port of the first header to each successively stacked cooling core along the second direction, wherein the first cooling core is configured to receive an intake airflow into the fluid-air heat exchanger along the second direction, and a second cooling core positioned furthest from the first cooling core within the plurality of stacked cooling cores is configured to exhaust the airflow from the fluid-air heat exchanger.
 23. The fluid-air heat exchanger of claim 22 wherein if a number of cooling cores is even, then the first fluid header includes an outlet port configured to output fluid received from the second cooling core.
 24. The fluid-air heat exchanger of claim 23 wherein the first header includes at least one divider to separate the inlet port from the outlet port.
 25. The fluid-air heat exchanger of claim 22 wherein if a number of cooling cores is odd, then the second fluid header includes an outlet port configured to output fluid received from the second cooling core.
 26. The fluid-air heat exchanger of claim 22 wherein the first header and the second header cumulatively include at least one fluid divider configured to direct fluid flow from the inlet port to the outlet port via the plurality of cooling cores.
 27. The fluid-air heat exchanger of claim 26 wherein the fluid flows between the first header, the second header, and from cooling core to cooling core in a serpentine-like manner.
 28. The fluid-air heat exchanger of claim 22 wherein a temperature of the input fluid is greater than a temperature of the fluid output from the outlet port.
 29. The fluid-air heat exchanger of claim 28 wherein a hot-to-cold fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 30. The fluid-air heat exchanger of claim 28 wherein a temperature of the intake airflow is colder than a temperature of the exhaust airflow.
 31. The fluid-air heat exchanger of claim 28 wherein a cold-to-hot air temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 32. The fluid-air heat exchanger of claim 22 wherein a temperature of the input fluid is less than a temperature of the fluid output from the outlet port.
 33. The fluid-air heat exchanger of claim 32 wherein a cold-to-hot fluid temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 34. The fluid-air beat exchanger of claim 32 wherein a temperature of the intake airflow is greater than a temperature of the exhaust airflow.
 35. The fluid-air heat exchanger of claim 32 wherein a hot-to-cold air temperature gradient is formed along the second direction from the first cooling core to the second cooling core.
 36. The fluid-air heat exchanger of claim 22 wherein each cooling core is exposed to a different temperature airflow.
 37. The fluid-air heat exchanger of claim 22 wherein the inlet port is positioned proximate a first end of the first fluid header, and the first cooling core is positioned proximate the first end of the first fluid header and a first end of the second fluid header.
 38. The fluid-air heat exchanger of claim 37 wherein the second cooling core is positioned proximate a second end of the first fluid header and a second end of the second fluid header.
 39. The fluid-air heat exchanger of claim 22 wherein each layer of fluid conduits comprises a plurality of individual thermally conductive micro-tubes, wherein each micro-tube is configured such that fluid flow therethrough is isolated from each other micro-tube.
 40. The fluid-air heat exchanger of claim 22 wherein each layer of fluid conduits comprises a plurality of individual thermally conductive micro-tubes, wherein each micro-tube includes one or more common openings with an adjacent micro-tube such that fluid flow therethrough is intermixed between adjacent micro-tubes.
 41. The fluid-air heat exchanger of claim 22 wherein each cooling fin is configured along the second direction.
 42. The fluid-air heat exchanger of claim 22 wherein each cooling core includes a plurality of core layers, each layer including at least one layer of cooling fins and a layer of at least one fluid conduit, further wherein each core layer within a given cooling core is stacked along a third direction that is perpendicular to the first direction and perpendicular to the second direction.
 43. A fluid-air heat exchanger comprising: a. a plurality of fluid-air cooling cores, each cooling core includes at least one layer of one or more thermally conductive fluid conduits and at least one layer of thermally conductive cooling fins coupled to the at least one fluid conduit layer and mounted to pass air through the fluid-air cooling core, wherein each fluid conduit is configured along a first direction from a first end of the cooling core to a second end of the cooling core, further wherein the plurality of cooling cores are stacked side by side in series along a second direction perpendicular to the first direction such that the fluid conduits of the plurality of cooling cores are configured in parallel; b. a first fluid header coupled to the first end of each cooling core, wherein the first header includes an inlet port configured to receive an input fluid; and c. a second header coupled to the second end of each cooling core, wherein the first header and the second header are configured to direct fluid flow in series from a first cooling core to each successively stacked cooling core along the second direction.
 44. The fluid-air heat exchanger of claim 43 wherein if a number of cooling cores is even, then the first fluid header includes an outlet port configured to output fluid received from a last cooling core in the series.
 45. The fluid-air heat exchanger of claim 44 wherein the first header includes at least one divider to separate the inlet port from the outlet port.
 46. The fluid-air heat exchanger of claim 43 wherein if a number of cooling cores is odd, then the second fluid header includes an outlet port configured to output fluid received from a last cooling core in the series.
 47. The fluid-air heat exchanger of claim 43 wherein the first header and the second header cumulatively include at least one fluid divider configured to direct fluid flow from the inlet port to the outlet port via the plurality of cooling cores.
 48. The fluid-air heat exchanger of claim 47 wherein the fluid flows between the first header, the second header, and from cooling core to cooling core in a serpentine-like manner.
 49. The fluid-air heat exchanger of claim 43 wherein each layer of fluid conduits comprises a plurality of individual thermally conductive micro-tubes, wherein each micro-tube is configured such that fluid flow therethrough is isolated from each other micro-tube.
 50. The fluid-air heat exchanger of claim 43 wherein each layer of fluid conduits comprises a plurality of individual thermally conductive micro-tubes, wherein each micro-tube includes one or more common openings with an adjacent micro-tube such that fluid flow therethrough is intermixed between adjacent micro-tubes.
 51. The fluid-air heat exchanger of claim 43 wherein each cooling fin is configured along the second direction.
 52. The fluid-air heat exchanger of claim 43 wherein each cooling core includes a plurality of core layers, each layer including at least one layer of cooling fins and a layer of at least one fluid conduit, further wherein each core layer within a given cooling core is stacked along a third direction that is perpendicular to the first direction and perpendicular to the second direction. 